Mellotron/Chamberlin Patents

The main six patents are by Harry Chamberlin, and additionally I've
also included the two Birotron patents. I'm intentionally
limiting the scope of this article avoiding patents for the Optigan,
Orchestron, samplers, and other technologies.

Links to the
US Patent and
Trademark Office are provided where you can find the text of the
patent, referencing data, and tiff scans of each page of the
patent. Unfortuantely most browsers will stumble on tiff
format images. I highly recommend using the
Pat2Pdf tool,
which retrieves the patent, gets the tiff scan images, compiles up a
pdf file, and presents it to you for downloading, and it prints up
great. So I've included links to that service for each patent
also.

The Patents

This is the first Chamberlin/Mellotron patent, and it somewhat
resembles a Mellotron-like device. There are tapes, heads, a
long capstain, multiple tracks, multiple "stations" or sections on
the tape, and a primitive mechanism to shuttle the tape between
the stations.

Some things to note:

The capstain is in the front of the unit instead of the rear
like production Mellotrons, and the tape runs toward the player
instead of away.

There's a switch on each key to switch the tape head in and
out of the circuit, presumably as an attempt at noise
reduction.

During playback, after the tape goes by the tape head, the tape
wraps around a wheel and tension on the tape is held by the
wheel dropping down a slot.

There's a brake mechanism to insert drops into the playback
sound.(!!!)

The motor drives the capstain with a friction roller drive; the
motor shaft extends out with a roller on the end, the roller
spins against the side of the flywheel, which is at the end of
the capstain roller.

The rewind mechanism is a pulley mounted on a large C-shaped
spring.

To shuttle the tape between stations you use this little
lever. Push the lever one way and the takeup drum spins,
push the lever the other way and the supply drum spins.
There's a marker on the tape at the beginning of each new
section and you have to work this lever back and forth until
you're in position.

There's some insanity in this patent. For one thing, it was
filed 16 October 1953, but the patent wasn't issued until almost
seven years later. That's a long time. So long that
Harry Chamberlin's next patent, a set of improvements to this one,
was issued before this one and so has an earlier patent
number.(!!!) So that's pretty confusing.

The drawings in the patent look absolutely nothing like a keyboard
instrument. Unless you're a major Mellotron fan, you'd
probably mistake the drawings for a cotten gin or something.

The text in the patent itself is written... well... here's a sample:

As further shown in Fig. 2, each tape extends rightwardly from
its idler 20, as indicated at 22 through a
guide 23, across the upper surface of a driving
roller 24 as shown at 25 over a guide
bar 26 and then over a suppporting plate 27 which
is curved around the upper righthand portion of the spool
means 11, downwardly as indicated at 28 and under
a small floating puller 29, as indicated at 30, to
a channel 12 in the spool means 11, in which the
rightward end of the tape is wound.

(Ah, where have the great writers gone? Yeah, I'm reading
through pages of this.)

This is the second Chamberlin/Mellotron patent, filed almost three
years after the first one, but since the first patent took so long
this was actually issued first. It covers improvements to
the implementation described in the first patent (although that's
hard to tell from the title) and appears to be very close to the
actual implemenation of the Chamberlin Model 200.

And the drawings still look nothing like a keyboard instrument.

Improvements include:

The tape playback reservoir box is introduced, replacing a wheel
sliding in a vertical slot. The rewind mechanism is now
much faster because the return spring is no longer working
against the weight of the wheel and you no longer have the
inertia from the mass of the wheel.

There's an interlock to keep from playing the instrument and
shuttling the tape at the same time and ripping the tape.

The shuttling mechanism seems to be improved, but the
description is far too confusing to tell what's going on.

There's an indicator tape that slides through a slot in the front
panel to help position the tape when changing stations.

For both of the drums, there's a screw adjustment for each note
that humps up the circumference of the channel that the tape
sits in a little bit to fine tune the station starting points
for that note.

And the whole mechanism has been turned around, so the tape
moves toward the rear of the unit during playback like
production Mellotrons. Ahhh.

The third Chamberlin/Mellotron patent with more
improvements. The drawings are slightly looking like a
keyboard instrument.

The split keyboard is introduced, "rhythm and harmony" on the
left keyboard, "melody" on the right keyboard. All three
outputs are available separately for stereo mixes.

One of the rhythm keys can be operated with a foot pedal, to
free the left hand for the harmony work.

Details about the construction that give you an understanding of
how the machine is used are finally revealed: the keyboard is 35
notes, G to F, the tape speed is 7 1/2 ips, the tapes are 8
seconds long, there are 3 tracks on the tape, there are 6
stations along the tape. The two keyboards can set their
stations independently. The rhythm, harmony and melody
sections can set their tracks independently. Examples of
the musical content of the tape are given.

The pulleys-and-long-springs rewind mechanism is introduced,
replacing the large C-shaped spring.

The track selection mechansim is introduced.

Electric station selection is introduced. An extra control
tape has holes punched in it at specific locations, electrical
contacts sense when the holes are in postion, some relay logic
decides which direction to move and drives the motor off,
forward or backward, and the motor drives a chain wrapped around
the two drums.

The fourth Chamberlin/Mellotron patent, and it's very similar to
the previous one in presentation and layout. The drawings
are very very close.

Here there is a discussion about recording the harmony tapes as
root-fifth-root for 12 notes up the chromatic scale, and then
three diminished chords for the next three keys. Playing one
of the third-less chords together with one of the three diminished
chords provides a way to get many chords out of 15 keys.

The track selection circuit is different here.

US Patent 3,278,188:
Multi-tape Reproducer with Single Pickup Head
Harry C. Chamberlin
Filed: 3 September 1963
Issued: 11 October 1966

This is a patent for the Chamberlin Rhythmate, the first drum
machine (at least the first one that doesn't involve actual
drums).

It's a tape-based drum machine. The tapes are in 6 foot
loops, nominally running at 7-1/2 inches per second. Since
tuning is less important for percussion sounds the tape speed can
be adjusted over a wide range of tempos. The tapes share a
single Mellotron-style roller capstain. A single tape head
is mounted with a pressure pad on a carriage that is movable
between the tapes; the user mechanically raises a lever and
positions it into one of the slotted positions.

Each tape has three tracks with compatible drum parts, and the
user can mechanically position the head to select individual
tracks or mixes of adjacent tracks.

The later model Chamberlins improved on the Mellotron's
pulleys-and-long-springs mechanism that rewinds the tape.

A motor drives a shaft perpendicular to the tapes, these wheels
are mounted on the shaft, one for each strip of tape, and the back
end of each tape is attached onto its wheel with a small fastener.
The wheels mount on the shaft with a ring of felt, so they slip.
There's a screwdriver adjustment on each wheel to set the amount
of slippage. The shaft spins opposite the tape, and the wheels
provide a roughly constant back force to rewind the tapes.

Advantages include a more constant rewind force than possible with
the pulleys-and-long-springs mechanism. Also since the tape
isn't sliding through plasitc pulleys there's less static charge
buildup. The wheels also a lot less room. A
disadvantage of the system is that you can't use it on instruments
with multiple stations.

It's the Birotron! This is a Mellotron-like instrument that
uses an array of commercial 8-track tape players to provide the
sound source. The keyboard is a simple organ keyboard, one
or two poles per key, and each key switch connects its tape player
output into the mix.

As a refresher, an 8-track tape cartridge holds 1/4-inch magnetic
tape spliced into a continuous loop. Inside the cartridge
the tape is wrapped around a single reel, pulled off the inside at
the hub, runs by the head, and is then wound back on the outside
of the reel. The playback head is stereo, and is
mechanically moved through four different positions. The tape
moves at 3-3/4 inches per second, there's about 10 minutes worth
of tape in the cartridge, so four head positions will get you
through an album.

In practice the Birotron might have 20 stereo 8-track tape
players, each supplying two notes, for a total of 40 notes on the
keyboard, and you can use the track selection mechanism to switch
between four different sounds.

Compared to a real Mellotron, the Birotron has no touch
sensitivity. The keyboard is just switches, and varying the
pressure applied to the keyboard does nothing. Also, since
the Birotron uses tape loops it's not possible to have sounds with
attacks or transients. On the other hand, it's possible to
play faster on a Birotron, and there's no 8 second time limit.

Also included in the patent is a technique for recording the
cartridges when the source material is a short tape loop.
The source loop is played on a machine with two playback heads and
a fader pot that sweeps between them, and the operator gets to
watch the splice and fade away from the head nearest the splice.

Rick Wakeman's Birotron patent is very similiar to David
Biro's. In fact, a number of paragraphs of the patent text
are identical or near identical.

In this version, the commercial 8-track tape players are replaced
with a single playback mechanism with a common roller for the
capstain. The tape heads are all mounted on a single bar,
and that bar can be mechanically switched between the four track
positions. 8-track tape cartridges plug into the rear of the
unit, all in a row, with little clamps to hold them in place.